Electric appliance comprising modules that can be juxtaposed

ABSTRACT

An electric appliance ( 1 ) comprising modules ( 2, 3 ) that can be juxtaposed to one another and interconnected using bridge elements ( 4 ) for transmitting electric signals and operating voltages. The modules ( 2, 3 ) and bridge elements ( 4 ) are provided with a pair of plug-in connectors ( 31 ) and also a pair of mating plug-in connectors ( 25, 26 ). The plug-in connectors ( 31 ) are each mounted in a cylindrical outer sleeve ( 36 ), and the mating plug-in connectors ( 25, 26 ) are mounted in cylindrical ducts or penetrations ( 19 ). An O-shaped sealing ring or gasket ( 38 ) is arranged about the circumference of each outer sleeve ( 36 ), so that the O-shaped gaskets ( 38 ) are under pressure when the outer sleeves ( 36 ) are inserted in the penetration ( 19 ) to interconnect the plug-in connectors ( 31 ) and the mating plug-in connectors ( 25, 26 ).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electrical apparatus withjuxtaposable modules which can be electrically connected to one anotherby bridge elements. More particularly, the present invention relates toproviding reliable connections between juxtaposable modules and bridgeelements using at least recesses with insertable sleeves and interposingsealing gaskets.

2. Description of the Related Technology

Prior Art apparatuses, as are known for example from DE 297 03 367 U1are often used as subscriber devices in bus systems for control andmonitoring of technical processes using sensors and actuators that canbe connected to the modules via apparatus connectors.

To seal the connecting site between the bridge elements and the modules,in the prior art the interfitting parts are made interlocking. One suchversion however, due to the required production precision, dictates highproduction costs. Nevertheless the attainable sealing effect is poor. Toimprove it, therefore in the known apparatus there is an additionalseal, for example, a flat seal, as is used in the apparatus known fromDE 296 07 525 U1, which when the bridge elements are inserted into themodules in the insertion direction, are pressed against the bottom partof blind recesses which is used as a contact carrier in the modulehousing. To produce the pressure required for this purpose, in the knownapparatus, there are threaded screws which are pushed through the holesof the bridge elements and can be screwed into threaded holes in themodular housing. Without this screw attachment the bridge elements,especially when these apparatuses are used on machines, would not bepositionally stable and the contact-making of the connectors would notbe resistant to vibrations.

SUMMARY OF THE INVENTION

The object of the invention is to devise an electrical device of theinitially mentioned type in which the connections for the bridgeelements and the modules have a permenance which meets high requirements(degree of protection IP 67) in a simple and economical manner, and thedisconnection force is as high as possible and vibration-resistant, andthe interconnection of the connectors is ensured without additionalfasteners.

This object is achieved by using at least recesses with insertablesleeves and interposing sealing gaskets.

By use of a cylindrical shape for penetrations, both economical andeffective O-shaped gaskets, e.g. rings, can be used as the sealingdevices; the O-shaped gaskets achieve their sealing force which actsessentially in the radial direction at a constant distance from thecontact surfaces solely by their dimensions and material properties anddo not require any additional features, such as more compression, orcontact surfaces such as abutments. Moreover, the O-shaped gaskets canbe very easily installed by being slipped onto the outside sleevessurrounding connectors or the mating connectors and do not need to beinserted into a blind recess or into grooves at the bottom part of blindrecesses, as in the apparatus known from DE 297 03 367 U1.

In addition, the penetrations can be produced much more economicallythan blind recesses. Bur mainly the penetrations and the pertinentcontact carriers can be located on separate parts of the electricalapparatus; this greatly simplifies both production and installation andenables versatile use. The penetrations are made either in the modulehousings or in the bridge elements, the pertinent contact carriersthereby independently can be included for example on circuit boardswithin the modules or bridge elements.

Furthermore, the outside sleeves which bear the O-shaped gasket are notform-fitted to the walls of the penetrations either, by which productionis greatly simplified and more economical.

The compressing force of the gasket for appropriate selection anddimensioning of the distances of the contact surfaces is so great thatforces for insertion and extraction of up to 10 kg are reached and thusin general no special additional features are necessary for sealing theattachment of the bridge elements. This has the advantage not only of asignificant reduction in production and installation costs, but alsoeasier handling, since the bridge elements, for example for replacementof modules in case of servicing, can be slipped on and withdrawn byhand.

By having an insertable outside sleeve integral with the bridge unit orthe module housing, without additional sealing features, ensurestightness also at the insertion sites of the outside sleeve into therespective penetration.

By incorporation of an oblique arrangement of the contact surfaces forthe O-shaped gasket, without any additional costs an increase of theinsertion and withdrawal forces up to roughly 15 kg which is independentof the O-shaped gasket composition and the relevant dimensions can beachieved, because the compression force of the gasket that is directedperpendicular to the contact surfaces includes a force component arisingfrom insertion due to the tilt of the contact surfaces. As a result ofthis increased withdrawal force on the one hand and thevibration-damping action of the elastic gasket on the other theresulting electrical apparatus is suited for mounting on the mountingsurfaces of highly vibrating machines without additional fasteningdevices.

One version of the module housing that provides structural dimensionscomparable to those of the bridge element and also includesplug-and-socket connections on the module housing for actuators, sensorsand a field bus enables a very compact apparatus with a low structuralheight which can also be used in many applications where there is littlespace available for installation.

By way of a partition extending from the module housing with acrosspiece, provides, if necessary, support for the bridge elementsslight tilting which is possible in extreme cases or in case ofunintentional bumping so that for these cases reliable sealing and ahigh withdrawal force are achieved. The dimensions are chosen such thatthe cited compactness of the module housing is preserved. Thisembodiment can be accomplished essentially without additional costs byone-piece production.

Another very simple and feasible embodiment of the apparatus of thepresent invention, has T-shaped projections and corresponding guideslots extend from the module housing so that the modules can be attachedto one another by hand (and if necessary can be detached from oneanother). Exact guidance of the projections into the slots moreoverensures that the center distances of the modules adjacent to the matingconnectors facing one another always corresponds exactly to that of theconnectors of the bridge elements, by which exactly centered axialinsertion of the connectors into the penetrations and thus optimumsealing and retaining action are ensured.

A console-shaped execution of the module housing has the advantage thatthe labeling fields and display elements positioned on the obliqueconsole surfaces are easily visible in the arrangement on or underroughly horizontal surfaces but also in a wall mounting. This is themore so when all labeling fields and display elements are located on thetilted console surface.

In another version of the module housing there are mounting feetextending from the module for resting on an installation surface.Between the housing bottom and the mounting surface there is a gapthrough which air flows (convection flow) which advantageouslydissipates the lost heat released from the encapsulated modules.Compared to the prior art according to German utility models 296 07 525and 297 03 367 in which the modules are located without spacing on themounting sheets, the operating temperature for the present invention islower and thus the service life of the modules is increased.

It is especially economical to produce the feet in one piece with themodule housing, for example in an injection molding process, and toprovide them at the same time with holes for screw attachment of themodules to mounting surfaces.

The convection flow between the housing bottom and the mounting surfaceand thus also the heat dissipation are especially strong when thehousing bottom is made trough-shaped and to taper toward housing endfaces.

A further intensification of cooling of the modules can be achievedincorporating elevations (domes) as part of the housing bottom in thathousing bottom has a surface as large as possible for heat dissipation,for which especially tubular domes are suited for the elevations(domes). The cross sections of the domes can be made in any shape, forexample, square or round.

A grid-like arrangement of these domes, by which corridors which run inthe flow direction between the domes are formed, moreover facilitatingthe dissipation of unwanted lost heat.

A one-piece execution of the domes and housing bottom not only reducesproduction costs, but also ensures optimum heat transfer from thehousing bottom to the dome surfaces.

Overall, a noticeable prolongation of the apparatus service life isachieved by incorporation at lease these features of mounting feet,housing bottom spaced from mounting surfaces, and elevations (domes)integrated as part of housing bottoms.

It is a good idea to use a circuit board for internal line connectionsand to accommodate electrical switching elements, which the board can beattached in the module housing very easily and economically by a pressfit.

Depending on the separation of the assigned mating connectors from theirpenetrations, the connectors can be mounted on the circuit board and indoing so their contact elements can be connected directly to thepertinent printed conductors of the circuit board without additionalconnecting lines.

In one advantageous embodiment of the bridge elements a connector tofeed an operating voltage independent of the bus lines into the modulesis enabled. Conductor cross sections can thus be adapted to [the] feedcurrents which are desired in the individual case. For example, they canbe designed for currents so high that a plurality of sensors andespecially actuators can be supplied. This is not possible in thetransmission of operating voltages via bus lines, for which reason forexample in the apparatus known from DE 296 07 525 U1 requires anadditional feed module ASI. When using bridge elements according to thisembodiment of the present the invention, no such device is necessary.

In many applications, for individual actuators and groups of actuatorsseparate operating voltage circuits are desired, for example when theoperating voltage for certain actuators in case of a hazard is to bedisconnectible on an emergency basis without influencing the remainingsubscribers over the bus line. This is enabled by formation of thebridge elements by having only one conductor for the operating voltage,which bridge elements are inserted on the pertinent modules simply andeconomically. With these bridge elements, flexible adaptation to thedifferent requirements of the individual case is thus achieved withrespect to the operating voltage supply. Conversely, in the knownapparatuses only a supply of all actuators and sensors is possible.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained below using one embodiment in the form of afield bus subscriber unit according to an alternative shown in thefigures.

FIG. 1 shows a perspective view of a field bus subscriber unit accordingto the present invention;

FIG. 2 shows a perspective view of an individual module without visiblemating connectors;

FIG. 3 shows a side view

(FIG. 3a), a plan view of the feed side

(FIG. 3b) and a plan view of the plug side

(FIG. 3c) of a bridge element; and,

FIG. 4 shows a section view through two modules connected to the bridgeelement.

DETAILED DESCRIPTION OF THE INVENTION

A field bus subscriber unit 1, as shown in FIG. 1, consists of the fieldbus terminal module 2 and four I/O (input/output) modules 3 for controland monitoring of actuators and sensors which are not shown, which areelectrically connected to one another and to the field bus terminalmodules 2 by internal signal and operating voltage lines via bridgeelements 4, and have plug-and-socket connections 5 for connection to theactuators and sensors.

The field bus terminal module 2 is connected to the field bus via twoconnectors 6 and on the one hand relays the sensor signals obtained fromthe I/O modules 3 via the internal signal lines to the field bus and onthe other hand supplies control signals decoupled from the field bus viathe I/O modules 3 to the actuators.

The I/O modules 3 have a console-shaped module housing 7 with a bottom 8and feet 9 and a circuit board 10 which bears the plug-and-socketconnections 5 which for their part pass through recesses 11 of the roofsurface 12 of the module housing 7 and are somewhat flush with them. Allthe labeling fields 42 and LED display elements 43 of the modules 2, 3are located on the console surface 13.

The module housing 7 and the field bus terminal module 2 on one sidewall 14 have two projections 15 which are T-shaped in cross section andin the opposite side wall 14′ of the I/O modules 3, guide slots 16 whichare open to the top and which are matched thereto. By inserting theprojections 15 of the module housing 7 into the guide slots 16 of theadjacent module housing 7 the I/O modules 3 and the field bus terminalmodule 2 can be juxtaposed to one another by hand.

On the end face opposite the console surface 13 the module housing 7 hasa shoulder 17 (see FIG. 4); in its base surface 18 there are twocollar-shaped penetrations 19 with a cylindrical wall 20. In the middlebetween the penetrations 19 of each module 3, between the end face 21 ofthe shoulder 17 and a crosspiece 23 which is flush with theterminal-side end face 22 of the module housing 7 there is a partition24, the height of the crosspiece 23 and the partition 24 corresponds tothat of the end face 21.

On the circuit board 10 there are two contact carriers 25 which are notshown in FIG. 2, with twenty eight receptacles 26 each (see FIG. 4),which are connected to the pertinent terminal points or printedconductors of the circuit board 10 and are positioned in the area of thepenetrations 19.

The feet 9 which have elongated holes 27 for optionally required screwattachment of the module housings 7 project from the bottom of thehousing 7 so that between the housing bottom 8 and the installationsurface there is an intermediate space in which an air flow forms, bywhich the lost heat forming in the encapsulated 1/O modules 3 and thefield bus terminal module 2 is largely dissipated. This advantageousaction is intensified by the housing bottom 8 being made trough-shaped,its tapering toward the end faces of the modules 2, 3 and having domes28 which are arranged in a grid; as a result of their large surface alarge amount of heat can be dissipated.

The bridge elements 4 each have a cuboidal housing body 29 and two28-pin connectors provided on the base surface 30, their center distanceand that between the penetrations 19 of the two adjacent I/O modules 3,which penetrations face one another, are the same. In two of the fourbridge elements 4 there are moreover 6-pin connector sockets 33.

The dimensions of the housing bodies 29 correspond to those of the spacebetween the partitions 24 of two adjacent modules 2, 3 and between thecrosspieces 23 and the end faces 21 of the shoulder 17, the coversurfaces 32 being flush with the roof surfaces 12 of the module housing7 when the bridge elements 4 are inserted.

The connectors 31 each consist of a carrier 35 which is integrated witha card 34 for holding the twenty eight plug pins 36 which correspond tothe receptacles 26 and an essentially cylindrical outside sleeve 37which encompasses them and which bears an O-shaped gasket 39 in theannular depression 38 of the jacket surface.

The inside wall 40 of the depression 38 and the penetration wall 20parallel to it in the module housing 7 are tilted at an angle of roughly10° to the plug axis. The tilt causes a force component in the insertiondirection so that together with the corresponding dimensioning of themutual distance of the contact surfaces 20, 40 and of the gasket 39 andits material properties, a high withdrawal force of roughly 15 kg isreached overall, by which installation of the field bus subscriber unit1 is enabled even on highly vibrating surfaces, for example of machines,without additional fastening devices.

The connector sockets 33 each have six contact pins 42 which are held inan insulating part 41, which are soldered on the card with continuingprinted conductors, and which are encompassed by a collar 46 whichprojects to the outside and which is integral with the housing body 29and the insulating part 41.

In assembling the field bus subscriber unit 1, first the field busterminal module 2 and the I/O modules 3 are juxtaposed to one another byinserting the T-shaped projections 15 which are attached to the sidewalls 14 until they pass into the guide slots 16 located on the sidewalls 14′ and if necessary are screwed with the feet 9 to theinstallation surface.

In this way, the module housings 7 are detachably fastened to oneanother in the set position, by exact, almost play-free guidanceespecially the exact theoretical distance of the penetrations 19 ofadjacent module housings 7, that is, the penetrations facing oneanother, being aligned so that the connectors 31 cannot tilt when thebridge elements 4 are subsequently inserted into the mating connectors25, 26 or cannot be inserted obliquely to the plug axes. In this way,the gaskets 38 are pressed on the entire periphery uniformly against thewalls 20 of the penetrations 19, by which the maximum sealing action isalways achieved.

When the I/O module 3 is located on the end of the field bus subscriberunit 1 the last mating connector which is not further connected by abridge element is covered by a blind cap 45.

The internal signal lines (printed conductors on the circuit boards 10)which are connected to the plug-and socket connections 5 of theactuators and sensors are guided through the I/O modules 3 via thereceptacles 26 of the mating connectors, the plug pins 36 of theconnectors 31 and the printed conductors on the circuit board 10 and thecard 34, and are supplied to the field bus terminal module 2.

Two of the four I/O modules 3 have a connector socket 33 by which theoperating voltage especially for the actuators is supplied via one ofthe connectors 31 of the bridge elements 4 to two separate actuatorcircuits which each encompass two I/O modules 3 and which can thus bedisconnected separately in case of emergencies.

The contact pins 42 of the connector sockets 33 are designed forcurrents of 8 Amperes (A) in this case. For their undisrupted routing tothe actuators several printed conductors on the card 34 and the circuitboard 10 as well as several of the thinner plug pins 36 and receptacles26 are connected in parallel.

Finally, the sensors and actuators are connected to the plug-and-socketconnections 5 of the field bus terminal module 2 and the I/O modules 3,and the field bus terminal module 2 is connected to the field bus usingthe connectors 6. With this simple and prompt installation the field bussubscriber unit 1 is serviceable. Replacement of modules in the fieldbus subscriber unit 1 of the present invention is also especially easilypossible, for example in a case of service or to adapt the entire unitto altered requirements, in contrast to the apparatus unit known from DE296 97 525 U1, regardless of the location of the individual module inthe entire combination. Simply by withdrawing two bridge elements 4 (inthe last I/O module 3 of the unit only one bridge element 4) by hand andoptionally loosening the screw connections on the module feet 9 anyindividual module can be removed from the combination and equallypromptly replaced.

What is claimed is:
 1. Electrical bus apparatus having a plurality ofplug-and-socket connectors, said electrical apparatus comprising: atleast two juxtaposable modules, each juxtaposable module having (i) amodule housing, (ii) at least one plug-and-socket connector, and (iii)at least one mating connector; at least one bridge elementinterconnected to said two juxtaposable modules to transmit electricalsignals and operating voltages, said bridge element having two bridgeconnectors, each of said bridge connectors being connected to one ofsaid mating connectors of said two juxtaposable modules; and, each ofsaid module housings having at least one cylindrical recess with amating connector disposed in said cylindrical recess, and each bridgeconnector having an essentially cylindrical outside sleeve with anO-shaped gasket disposed in an annular depression that is disposed abouta periphery of said cylindrical outside sleeve with said O-shaped gasketunder pressure contacting a gasket contact wall of said cylindricalrecess.
 2. Electrical apparatus as claimed in claim 1, wherein eachcylindrical outside sleeve is integral with the bridge element. 3.Electrical apparatus as claimed in claim 1, wherein the gasket contactwalls of the cylindrical recesses are essentially parallel to theannular depressions, and said gasket contact walls are tilted from aconnector axis.
 4. Electrical apparatus as claimed in claim 1, whereinthe module housing includes a shoulder extending from a base surface toa height from said base surface that corresponds to that of a housingbody of the bridge element interconnected to said module.
 5. Electricalapparatus as claimed in claim 1, wherein the plug-and-socket connectorsare countersunk in each module housing with an upper surface for eachplug-and-socket connector being about flush with a roof surface of saidmodule housing.
 6. Electrical apparatus as claimed in claim 1, whereineach of said module housings includes: a first opposite side wall and asecond opposite side wall; at least one T-shaped projection extendingfrom said first opposite side wall; at least one guide slot having anopening extending toward a roof surface of the module housing, and saidguide slot extending from said second opposite side wall; and said twojuxtaposable modules interconnected by said T-shaped projectionextending from a first of said two juxtaposable modules being disposedinto the opening of said guide slot extending from a second of said twojuxtaposable modules.
 7. Electrical apparatus as claimed in claim 1,wherein each of the module housings includes at least one labeling fieldand at least one display element, both mounted on an inclined surface ofsaid module housing.
 8. Electrical apparatus as claimed in claim 1,wherein at least two feet extend from each of the module housings, andeach of said feet has a support surface disposed for resting on aninstallation surface, said support surfaces further being disposed at adistance away from a housing bottom of said module housing. 9.Electrical apparatus as claimed in claim 1, wherein each of thejuxtaposable modules includes one circuit board from which a matingconnector is disposed and to which plug-and-socket connectors areelectrically connected.
 10. Electrical apparatus as claimed in claim 1,wherein the bridge element has an additional connector socket disposedfor connection to an operating voltage source.
 11. Electrical apparatusas claimed in claim 4, wherein the module housing further includes apartition and a crosspiece that both extend away from said base surfacewith said partition extending transverse from said shoulder and saidcrosspiece extending transverse from said partition, said crosspiecehaving a surface that is flush with a terminal-side end face of themodule housing, the heights of both the crosspiece and the partitionfrom the base surface being about that of the shoulder.
 12. Electricalapparatus as claimed in claim 11, wherein the crosspiece and thepartition are integral with the module housing.
 13. Electrical apparatusas claimed in claim 9, wherein the circuit board is press fit into themodule housing.
 14. Electrical apparatus as claimed in claim 10, whereinthe bridge element includes conductors for transmission of the operatingvoltage, said conductors being routed and connected to only one bridgeconnector.
 15. Electrical apparatus as claimed in claim 8, wherein thefeet are integral with the module housing, and each foot includes anopening with a mounting screw disposed in said opening.
 16. Electricalapparatus as claimed in claim 15, wherein the housing bottom istrough-shaped and tapers toward two opposite end faces of the modulehousing.
 17. Electrical apparatus as claimed in claim 16, wherein thehousing bottom includes multiple domes arranged in a grid. 18.Electrical apparatus as claimed in claim 17, wherein the domes areintegral with the housing bottom.
 19. Electrical apparatus as claimed inclaim 17, wherein the domes are tubular shaped.
 20. Electrical apparatusas claimed in claim 19, wherein the domes are integral with the housingbottom.
 21. Electrical bus apparatus having a plurality ofplug-and-socket connectors, said electrical apparatus comprising: atleast two juxtaposable modules, each juxtaposable module having (i) amodule housing, (ii) at least one plug-and-socket connector, and (iii)at least one mating connector; at least one bridge elementinterconnected to said two juxtaposable modules to transmit electricalsignals and operating voltages, said bridge element having two bridgeconnectors, each of said bridge connectors being connected to one ofsaid mating connectors of said two juxtaposable modules; and, saidbridge element having two cylindrical recesses with a bridge connectordisposed in each of said cylindrical recesses, and each mating connectorhaving an essentially cylindrical outside sleeve with an O-shaped gasketdisposed in an annular depression that is disposed about a periphery ofsaid cylindrical outside sleeve with said O-shaped gasket under pressurecontacting a gasket contact wall of said cylindrical recess. 22.Electrical apparatus as claimed in claim 21, wherein each cylindricaloutside sleeve is integral with the module housing.
 23. Electricalapparatus as claimed in claim 21, wherein the gasket contact walls ofthe cylindrical recess are essentially parallel to the annulardepressions, and said gasket walls are tilted from a connector axis. 24.Electrical apparatus as claimed in claim 21, wherein the module housingincludes a shoulder extending from a base surface to a height from saidbase surface that corresponds to that of a housing body of the bridgeelement interconnected to said module.
 25. Electrical apparatus asclaimed in claim 21, wherein the plug-and-socket connectors arecountersunk in each module housing with an upper surface for eachplug-and-socket connector being about flush with a roof surface of saidmodule housing.
 26. Electrical apparatus as claimed in claim 21, whereineach of said module housings includes: a first opposite wall and asecond opposite wall; at least one T-shaped projection extending fromsaid first opposite side wall; at least one guide slot having an openingextending toward a roof surface of the module housing, and said guideslot extending from said opposite side wall; and said two juxtaposablemodules interconnected by said T-shaped projection extending from afirst of said two juxtaposable modules being disposed into the openingof said guide slot extending from a second of said two juxtaposablemodules.
 27. Electrical apparatus as claimed in claim 21, wherein eachof the module housings includes at lest one labeling field and at leastone display element, both mounted on an inclined surface of said modulehousing.
 28. Electrical apparatus as claimed in claim 21, wherein atleast two feet extend from each of the module housings, and each of saidfeet has a support surface disposed for resting on an installationsurface, said support surfaces further being disposed at a distance awayfrom a housing bottom of said module housing.
 29. Electrical apparatusas claimed in claim 33, wherein the housing bottom is trough-shaped andtapers toward two opposite end faces of the module housing. 30.Electrical apparatus as claimed in claim 21, wherein each of thejuxtaposable modules includes one circuit board from which a matingconnector is disposed and to which plug-and-socket connectors areelectrically connected.
 31. Electrical apparatus as claimed in claim 21,wherein the bridge element has an additional connector socket disposedfor connection to an operating voltage source.
 32. Electrical apparatusas claimed in claim 24, wherein the module housing further includes apartition and a crosspiece that both extend away from said base surfacewith said partition extending transverse from said shoulder and saidcrosspiece extending transverse from said partition, said crosspiecehaving a surface that is flush with a terminal-side end face of themodule housing, the heights of both the crosspiece and the partitionfrom the base surface being about that of the shoulder.
 33. Electricalapparatus as claimed in claim 28, wherein the feet are integral with themodule housing, and each foot includes an opening with a mounting screwdisposed in said opening.
 34. Electrical apparatus as claimed in claim29, wherein the housing bottom includes multiple domes arranged in agrid.
 35. Electrical apparatus as claimed in claim 30, wherein thecircuit board is press fit into the module housing.
 36. Electricalapparatus as claimed in claim 31, wherein the bridge element includesconductors for transmission of the operating voltage, said conductorsbeing routed and connected to only one bridge connector.
 37. Electricalapparatus as claimed in claim 32, wherein the crosspiece and thepartition are integral with the module housing.
 38. Electrical apparatusas claimed in claim 34, wherein the domes are tubular shaped. 39.Electrical apparatus as claimed in claim 34, wherein the domes areintegral with the housing bottom.
 40. Electrical apparatus as claimed inclaim 38, wherein the domes are integral with the housing bottom.